The first version of zsh was written by Paul Falstad in 1990 when he was a student at Princeton University. The name zsh derives from Zhong Shao, then a teaching assistant at Princeton University. Paul Falstad thought that Shao’s login name, “zsh”, was a good name for a shell.

Features of note include:

Programmable command line completion that can help the user type both options and arguments for most used commands, with out-of-the-box support for several hundred commands

Various compatibility modes, e.g. zsh can pretend to be a Bourne shell when run as /bin/sh

Themeable prompts, including the ability to put prompt information on the right side of the screen and have it auto-hide when typing a long command

Fully customizable

Attesting to the sheer size of this shell is the first sentence of the shell’s manual page, which reads “Because zsh contains many features, the zsh manual has been split into a number of sections”, and then goes on to list thirteen items.